Hello!
I’m trying to start training with my new Edge 1040. Synced Garnin Connect with Intervals.ICU, sent workout to edge 1040 and that it’s. How I must act.
Training / Smart Trainer / Follow Workout / Start button and it’s always 122 watts resistance with no erg mode enabled.
Profile: Indoor
Trainer: Tacx Flux S
It was almost ideal with Wahoo Elmnt bolt 
I’m not going to try help resolve your problem, as I don’t have experience with either device (Edge and Tacx). I’m sure someone will tell you what’s missing.
I am going to tell you instead, that riding off ERG mode will help your “feel” for the workout levels. You will benefit much more by not using ERG.
The problem was in “ramp 40-50%” command. It’s weird but Garmin doesn’t understand it.
Garmin also averages a range too, example 110-120% will show 115% on your workout, or 65-74% will be 69.5%
The problem comes where heart rate decouples from power (even at high power). Being able to do the right power and keep HR in check is one of the limitations of ERG mode.
Is this where having HR controlling Power would be ideal?
Tho, most times, HR and Power doesn’t jive, esp for me at the lower end of HR (z1/Z2 stuffs)
You could do workouts by HR in the TACX app before Garmin bought them. But that option was removed as the app was updated post Garmin.
It’s not so much about HR controlling power but rather the physiological benefit of staying close to, or under the limit. The long term benefit, is being able to get more power at the same HR.
Excluding the age factor, a ton of time and some genetics, there’s a reason a Pro can do 300W up a climb and still be in Z2.